1. Field of the Invention
The present invention relates to medical devices in general and more particularly to a portable device and a method for determining whether the blood sample extracted from the patient's body is arterial or venous.
2. Discussion of the Related Art
People who are extremely ill or injured are often admitted for medical care through a hospital's emergency room (ER). In administering emergency care medicine in an ER, time is a very valuable commodity. The patient's well being and even life may depend on rapid administration of proper medical care. Central Venous Catheters, also known as “Central lines”, are most commonly used for administration of IV fluids, antibiotics, blood transfusions, nutritional supplements, or medications used to support and improve blood pressure, which are optimally delivered through central lines. These catheters are also important for checking serial blood tests and monitoring the fluid and hydration status of the patient. In emergency and critical care medicine, these catheters are vital for resuscitation, monitoring, and optimal management of critically ill patients.
Central line catheters are long and large bore catheters and are designed to be inserted into veins. Veins are low pressured and return blood from organs and tissues to the heart and arteries are high pressured and carry oxygenated blood to organs and bodily tissues. Central lines are inserted into the large veins of the body, typically one of three large veins such as the internal jugular vein (located in the neck), the subclavian vein (located in the chest), or the femoral vein (located in the groin). These large veins run next to major arteries; the internal jugular runs alongside the carotid artery in the neck, the subclavian vein runs alongside the subclavian artery in the chest, and the femoral vein runs alongside the femoral artery in the groin area.
To accomplish the insertion of a central line, the patient is properly positioned and the insertion area is sterilized. The medical professional uses either anatomic landmarks or ultrasound to identify the location of the vein for insertion. The area is anesthetized and an ‘introducer needle’ connected to a syringe is advanced until the tip of the needle is in the desired vein. Placement of the needle in the vein is confirmed by aspiration of blood into the syringe. A guide wire and a dilator tube are then introduced to guide the catheter in place at which time the catheter is sutured in place. Appropriate positioning of the catheter is confirmed by taking a chest x-ray.
Because of the proximity of the vein to the corresponding artery, a major risk during the insertion of central lines is accidental arterial cannulation, or the advancement and placement of the catheter into a large artery instead of the vein. Arterial cannulation has potential catastrophic implications including hemothorax (bleeding into the chest cavity), carotid, subclavian, or femoral artery injury, stroke, and even death. Thus, ER personnel are intent on distinguishing arterial versus venous blood prior to cannulating with the dilator and inserting and suturing the catheter. Current methods of distinguishing venous from arterial blood are inaccurate, unreliable, or impractical.
The most common method of distinguishing venous from arterial blood during catheter placement is visual analysis. Arterial blood is classically a brighter red and more pulsatile in comparison to venous blood. However, these characteristics are very subjective and thus unreliable. The color of a patient's blood sample can be incorrectly interpreted depending on a variety of factors such as the patient's blood oxygenation, past medical history, operator experience, and even the ambient lighting in the room where the procedure is performed. Further, ill patients receiving central lines often have low blood pressure who would not exhibit classic pulsatile arterial blood flow to distinguish arterial blood from venous blood.
Another method is the use of blood gas analysis. In this method, a sample of blood is placed in a machine and after analysis the machine displays the amount of oxygenation. While accurate, blood gas analysis is not easily available and is time consuming. In many hospitals, this test is only performed in a laboratory and can take five minutes or more to obtain results. If the patient is in need of emergency care, proper care often requires more immediate action than available when the care givers must wait on machine analysis.
Pressure waveform monitoring is also used to determine the source of a blood sample. However, this method is limited because most cardiac monitors do not have this option available. Also, this method is time consuming to set up and requires additional people to complete the process. Since this method depends on the pressure of the blood sample to distinguish between arterial and venous blood, low blood pressure in some sick patients can cause unreliable results.
Another method to aid in the placement of the catheter is the use of ultrasound. This method has been shown to reduce patient discomfort and the number of arterial sticks. Because of the high pliancy of vessel walls, veins tent and collapse when the central line is being placed. Even under ultrasound guidance, the medical professional can puncture through the vein resulting in arterial insertion. Therefore, ultrasound guidance does not offer the reliability desired to readily distinguish arterial blood from venous blood.
Although there are various studies published in medical journals that provide a comparison of arterial and venous blood gas values before, during, and after the operation of the patient, none of that information is utilized in developing a method or a device to place central line kits efficiently, safely and accurately within the patient's body. Thus what is desired is a testing device that can readily distinguish between arterial and venous blood in minimal time and at the patient's bedside quickly and accurately to facilitate the placement of central line kits in an emergency situation.